Crop productivity is influenced by many factors, among which are, on the one hand factors influencing the capacity of the plant to produce biomass (photosynthesis, nutrient and water uptake), and on the other hand factors influencing the capacity of the plant to resist certain stresses, like biotic stresses (insects, fungi, viruses . . . ) or abiotic stresses (drought, salinity . . . ).
One important factor influencing the production of biomass is photosynthesis. Photosynthesis is the mechanism through which plants capture atmospheric carbon dioxide and fix it into carbon skeletons that are used for biosynthesis. The vast majority of plant species fix atmospheric CO2 using the enzyme ribulose bisphosphate carboxylase/oxygenase (Rubisco) in the Calvin-Benson cycle. The first stable product of this cycle is a three-carbon compound, phosphoglycerate (3-PGA), and thus, this process is referred to as the C3-cycle. Regeneration of the RuBP involves eight enzymes including sedoheptulose 1,7-bisphosphatase (SBPase). Small reductions in the SBPase resulted in a decrease in CO2 fixation and growth, identifying this enzyme as a control point in the C3 cycle. A major problem with the C3 cycle is the enzyme Rubisco. Rubisco is not only an inefficient enzyme with a low turnover number, but it also catalyses two competing reactions: carboxylation and oxygenation of RuBP. The oxygenation reaction directs the flow of carbon through the photorespiratory pathway and can result in losses of between 25-30% of the carbon fixed. Environmental variables, such as high temperature and drought, can result in an increase in the oxygenase reaction. (for a review see Raines 2011 Plant Physiology vol 155, pp 36-42).
To improve crop photosynthesis, one strategy is to overcome the oxygenase reaction of Rubisco by creating a photorespiratory bypass in the chloroplast through expression of glycolate catabolizing enzymes.
WO2003/100066 relates to a method for the production of plants with suppressed photorespiration and improved CO2 fixation. In particular, the invention relates to a re-use of phosphoglycolate produced in photorespiration. The reaction product will be converted to a component that may be reintegrated into the plant assimilatory metabolism inside the chloroplast. This is accomplished by the transfer of genes derived from glycolate-utilizing pathways from bacteria, algae, plants and/or animals including humans into the plant nuclear and/or plastidial genome. The method leads to a reduction of photorespiration in C3 plants and by this will be of great benefit for food production especially but not exclusively under non-favourable growth conditions.
WO2010/012796 relates to a method for stimulating the growth of the plants and/or improving the biomass production and/or increasing the carbon fixation by the plant comprising introducing into a rice plant cell, rice plant tissue or rice plant one or more nucleic acids, wherein the introduction of the nucleic acid(s) results inside the chloroplast of a de novo expression of one or more polypeptides having the enzymatic activity of a glycolate dehydrogenase.
WO2011/095528 relates to a method for stimulating the growth of the plants and/or improving the biomass production and/or increasing the carbon fixation by the plant comprising introducing into a plant cell, plant tissue or plant one or more nucleic acids, wherein the introduction of the nucleic acid(s) results inside the chloroplast of a de novo expression of one or more polypeptides having the enzymatic activity of a glycolate dehydrogenase made up from translationally fused subunits of bacterial multi-subunit glycolate dehydrogenase enzymes.
Kebeish et al. (2007 Nature Biotechnology Vol 25, pp 593-599) reported that the photorespiratory losses in Arabidopsis thaliana can be alleviated by introducing into chloroplasts a bacterial pathway for the catabolism of the photorespiratory substrate, glycolate. The authors first targeted the three subunits of Escherichia coli glycolate dehydrogenase to Arabidopsis thaliana chloroplasts and then introduced the Escherichia coli glyoxylate carboligase and Escherichia coli tartronic semialdehyde reductase to complete the pathway that converts glycolate to glycerate in parallel with the endogenous photorespiratory pathway. This step-wise nuclear transformation with the five Escherichia coli genes leads to Arabidopsis plants in which chloroplastic glycolate is converted directly to glycerate. These transgenic plants grew faster, produced more shoot and root biomass, and contained more soluble sugars. An effect was also visible but to a lesser extent in Arabidopsis plants that overexpressed only the three subunits of the glycolate dehydrogenase.
Nölke et al. (2014 Plant biotechnology Journal, Vol 12, pp 734-742) described the expression of a recombinant glycolate dehydrogenase polyprotein in potato (Solanum tuberosum) plastids which strongly enhances photosynthesis and tuber yield.
Another strategy to try to improve crop photosynthesis could be the overexpression of sedoheptulose 1,7-bisphosphatase to increase the RuBP regenerative capacity of the Calvin cycle.
WO00/70062 describes expression of sedoheptulose 1,7-bisphosphatase in transgenic plants. Sedoheptulose 1,7-bisphosphatase (SBPase) is an enzyme catalyzing the reaction converting sedoheptulose 1,7-bisphosphate into sedoheptulose 7-phosphate. This enzyme is located in the chloroplast in leaves and stems. Overexpression of SBPase in transgenic plants is provided to improve plant yield by increasing leaf starch biosynthetic ability and sucrose production. Deregulated variants of the enzymes are also provided.
Miyagawa et al. (2001 Nature Biotechnology Vol 19 pp 965-969 reported that overexpression of cyanobacterial fructose 1,6-/sedoheptulose 1,7-bisphosphatase in tobacco enhances photosynthesis and growth.
Lefebvre et al. (2005 Plant Physiology Vol. 138 pp 451-460) reported that increased sedoheptulose 1,7-bisphosphatase activity in transgenic tobacco plants stimulates photosynthesis and growth at an early stage in development.
Lawson et al. (2006 Plant, Cell and Environment Vol 29, pp 48-58) described that decreasing SBPase alters growth and development in transgenic tobacco plants.
Tamoi et al (2006 Plant Cell Physiol, 47: 380-390) described the contribution of Fructose-1,6-bisphosphatase and Sedoheptulose-1,7-bisphosphatase to the photosynthetic rate and carbon flow in the calvin cycle in transgenic plants.
Feng et al. (2007 Plant Cell Reporter Vol 26, pp 1635-1646) reported overexpression of SBPase enhancing photosynthesis under high temperature stress in transgenic rice plants. In contrast to the results with tobacco, increasing SBPase activity in rice did not lead to increasing photosynthesis or growth. However, when the plants were subjected to heat or salt stress, higher photosynthesis rates were found in the transgenic plants, compared to wild-type controls under similar conditions.
There is therefore still a need for an efficient method for increasing the carbon fixation in plants, particularly crop plants, which increases the photosynthetic carbon assimilation and stimulates the growth of the plant and/or improves biomass and/or seed production.